JP2998093B2 - Acetal resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides an extremely high degree of mold release during injection molding without impairing the mechanical properties, thermal stability, and appearance of molded products of acetal resins. The present invention relates to an acetal resin composition which is improved and has extremely small distortion of a precision molded product.

Acetal resins have well-balanced mechanical properties, excellent abrasion resistance, excellent thermal stability, and extremely good fluidity. Often used as mechanical parts or precision mechanical parts.

In the case of a molded product with such a complex formation, the release of the molded product must be as smooth as possible.If the product is released with an excessively strong force, the product may be damaged or molding distortion may occur. Since the result is very unfavorable in that it is stored in the molded product and exposed during long-term use, it is extremely undesirable.

In addition, when molded by an injection molding machine, acetal resin has a relatively fast crystallization rate, and is relatively high in crystallization, and further has a different directionality when flowing the resin, so that it is compared with general amorphous resin. Mold distortion is likely to occur, especially in precision molded products such as pulleys and gears, which appear as surface run-out, causing uneven rotation and noise during practical use, and also cause stress cracking of molded products during long-term use. obtain.

[Prior art] One or more polyhydric alcohol fatty acid esters derived from a polyhydric alcohol having 2 to 10 carbon atoms and a higher fatty acid having 22 to 32 carbon atoms, which the present inventors have previously added, are added. Or an acetal resin composition obtained by adding at least one kind of the polyhydric alcohol fatty acid ester and at least one kind of higher fatty acid amide having a straight chain having 10 or more carbon atoms [Japanese Patent Application Laid-Open No. 63-0295661]. ] Highly improves the releasability at the time of injection molding of the acetal resin. However, although this resin composition has sufficient release properties, the effect of reducing the molding distortion of a molded article is not practically sufficient.

As a measure to reduce the molding distortion of the injection molded product, a method of reducing the molecular weight of the acetal resin for the purpose of improving the flowability, and Japanese Patent Publication No. 37-8816, Japanese Patent Publication No. 37-8815, and Japanese Patent Publication No.
37-16174 proposes a method of lowering the melt viscosity by adding a polyalkylene glycol and glycerin to an acetal resin, respectively.

However, in the composition obtained by the above-mentioned known technique, it is inevitable that the most important properties inherent in the acetal resin, such as mechanical properties and thermal stability, are slightly impaired. The improvement effect on moldability was hardly recognized, and it was recognized that the effect was poor in terms of reducing warpage and surface runout in precision molded products such as pulleys. Further, JP-A-57-128740 discloses a polyalkylene glycol alkyl ether and / or
Alternatively, an improvement measure by adding a polyglycerin fatty acid ester has been proposed. However, even in such a composition, the effect of improving the releasability is small.
It has been recognized that the effect is not sufficiently practical in terms of reducing distortion in a molded product having a complicated structure such as a gear and obtaining a molded product with small warpage and surface runout.

[Problems to be Solved by the Invention] However, an object of the present invention is to substantially eliminate the mechanical properties and thermal stability inherently of an acetal resin,
It is an object of the present invention to provide an acetal resin composition having a very high degree of releasability at the time of injection molding and having a small molding distortion of a precision molded product.

[Means for Solving the Problem] The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that the general formula R ₁ -O-(-R ₂ -O-) _m -R ₃ [where R ₁ Represents hydrogen or an aliphatic hydrocarbon group having 1 to 7 carbon atoms and an aryl group, R ₂ represents an ethylene group or a propylene group, and R ₃ represents a carbon atom having 1 carbon atom.
And m is an integer of 20 or more, and at least 0.01 to 5 parts by weight of a terminally etherified polyalkylene glycol represented by the following formula: By adding at least 0.01 to 2.0 parts by weight of a polyhydric alcohol fatty acid ester derived from a polyhydric alcohol and a higher fatty acid having 22 to 32 carbon atoms to the acetal resin, the original mechanical properties and thermal stability of the acetal resin It has been found that an acetal resin composition having extremely improved mold releasability at the time of injection molding and having extremely small distortion of a precision molded product can be obtained without impairing the properties and appearance of the molded product at all.

Examples of the terminally etherified polyalkylene glycol represented by the above general formula, R ₁ —O — (— R ₂ —O—) _m —R ₃ used in the present invention include the following compounds. Polyethylene glycol glycol allyl ether, polyethylene glycol glycol dimethyl ether, polyethylene glycol diallyl ether, polyethylene glycol diethyl ether, polyethylene glycol nonylphenyl benzyl ether,
Polyethylene glycol propyl ether, polyethylene glycol methyl ether, polypropylene glycol methyl ether and the like.

The polyhydric alcohol fatty acid ester used in the present invention is a polyhydric alcohol having 2 to 10 carbon atoms and 22 to 32 carbon atoms.
Is a compound having one or more ester groups derived from a higher fatty acid of
Glycerin, pentaerythritol, sorbitan, ethylene glycol, diethylene glycol, trimethylolmethane, triethylolmethane and the like are suitable. As higher fatty acids, behenic acid, cellotic acid, montanic acid, lacceric acid and the like are suitable.

The amount of the terminally etherified polyalkylene glycol added to the acetal resin is 0.01 to 5 parts by weight, preferably 0.02 to 3.0 parts by weight, based on 100 parts by weight of the acetal resin. The amount of polyhydric alcohol fatty acid ester added is 0.01
To 2.0 parts by weight, and the total amount of the terminally etherified polyalkylene glycol and the polyhydric alcohol fatty acid ester is preferably 0.02 to 3.5 parts by weight. If the total amount of both is less than 0.01 part by weight, the effect is practically insufficient, and if it exceeds 5 parts by weight, the thermal stability of the acetal resin and the appearance of the molded product are adversely affected.

The acetal resin used in the present invention refers to an oxymethylene unit or substantially an oxymethylene unit produced from a cyclic oligomer such as a trimer (trioxane) or tetramer (tetraoxane). Methylene homopolymer, and oxyalkylene units having 2 to 8 carbon atoms produced from the above raw materials and a cyclic ether such as ethylene oxide, propylene oxide, epichlorohydrin, 1.3-dioxolan, 1.3-dioxepane, glycol formal, or diglycol formal. Oxymethylene copolymer containing 0.1 to 20 parts by weight of

The acetal resin in the present invention can be subjected to a thermal stabilization treatment by a known method. For example, in the case of an oxymethylene homopolymer, a method of acylating a terminal OH group with a carboxylic anhydride is used. (For example, the method disclosed in JP-B-33-6099).

In the case of an oxymethylene copolymer, a method for stabilizing a copolymer or a copolymer composition by heating and melting to remove volatile components (for example, Japanese Patent Publication No.
8071) and a stabilization method by hydrolysis (for example, a method disclosed in Japanese Examined Patent Publication No. 40-10435), and any of these methods can be employed.

Further, to the composition of the present invention, known heat stabilizers, antioxidants, ultraviolet absorbers, and pigments, fillers, and conventionally known additives are also added as long as the effects of the present invention are not impaired. I can do it.

Although various methods for producing the acetal resin composition of the present invention can be adopted, it is essential to mix or melt-knead the components.

As an apparatus used for the melt kneading, a general kneader such as various extruders, kneaders, Banbury mixers, mixing rolls, etc. is used. As a kneading method at that time, a gentle mixing such as a V-shaped blender is used. Dry blending with a high-speed fluid mixing apparatus such as an apparatus or a Henschel mixer, or a method in which a mixture obtained by stirring and mixing in a state of a solution, an emulsion, or a suspension and then drying is charged into the kneading machine, Various methods such as a method of adding the polyhydric alcohol fatty acid ester of the terminally etherified polyalkylene glycol to the acetal resin composition in a homogeneous molten state in a kneader can be used.

The temperature of the melt-kneading is appropriately selected depending on the type of acetal resin to be used, various conditions such as the function of the mixing and kneading apparatus, and the purpose, but is in a temperature range from the melting point of the acetal resin to the decomposition temperature, generally 175 ° C. ~ 230 ° C is appropriate.

[Effects of the Invention] The acetal resin composition obtained according to the present invention has extremely high releasability at the time of injection molding without impairing the mechanical properties, heat stability, and appearance of the molded article originally possessed by the acetal resin. While being highly improved, the acetal resin composition obtained according to the present invention makes it possible to obtain a precision molded product having extremely small distortion.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following description, the intrinsic viscosity [η] is
The value measured at 60 ° C. in P-chlorophenol to which 2% by weight of α-pinene was added, and the added amount [phr] means parts by weight per 100 parts by weight of the acetal resin.

Examples 1 to 12 2.5 units of copolymerized units derived from ethylene oxide
Acetal resin [[η] = 1.1 dl / g] which is an oxymethylene copolymer containing 0.2% by weight of melanin as a thermal oxidation stabilizer, 0.2 phr of triethylene glycol-bis-
0.5 phr of [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionate] and 0.1 phr of magnesium hydroxide were mixed. To this mixture, the types and amounts of terminally-etherified polyalkylene glycol and polyhydric alcohol fatty acid ester described in Table 1 and Table 2 were added and mixed.

The obtained mixture mainly composed of an oxymethylene copolymer is subjected to a heat stabilization treatment using a vented twin-screw extruder (PCM-30 manufactured by Ikegai Iron Works) having an L / D of 30 mm and a screw diameter of 30 mm to obtain an oxymethylene copolymer composition. Was manufactured.

In addition to measuring the thermal stability of the sample obtained here and the releasability during injection molding, a molded article (test sample) described below
Is molded and fabricated, and the tensile strength and surface runout are measured.
The results shown in Tables Examples 1 to 12 were obtained. The measurement was performed as follows.

[Release force] Test molding conditions Injection molding machine; Toshiba IS-90B Injection pressure; 800kg / cm ² Mold temperature; 60 ° C Molded sample shape Height 27mm, outer diameter 34mm, thickness 2mm Cylindrical mold with bottom A molded product obtained by injection molding using an injection molding machine [TOSHIBA IS-90B] was connected to a protruding pin positioned at the center of the cylindrical bottom of the molded product by protruding a pin from the mold and releasing resistance when releasing the mold. The measurement was performed using a sensor (manufactured by Techno Plus Co., Ltd.).

[Surface Deformation] Two types of molded articles [test sample (1) and test sample (2) were prepared and measured.

Test sample (1)-Molded product shown in FIGS. 1-1 and 1-2 [test sample,
A disc having a diameter of 40 mm, an outer peripheral part thickness of 5 mm, and a center hole diameter of 3 mm] was molded and produced under the following two conditions.

Molding conditions Molding machine; Toshiba IS-90B Cylinder temperature; Approx. 200 ° C Mold temperature; Approx. 60 ° C Injection pressure: 550 kg / cm ² Boost time; 8 seconds Cooling time; Condition 7 seconds Condition 14 seconds ・ Measurement method Obtained The surface blur of the test sample (1) 1 was measured as shown in FIG. That is, a cylindrical jig 2 having a length of about 40 mm having an outer diameter corresponding to the inner diameter of the center hole is passed through the center hole of the test sample (1) 1, and the test sample (1) 1 and the jig 2 are connected to each other by 360.な が ら Slowly rotate the test sample (1)
The value of a digital micrometer 3 (Magnescale manufactured by Sony Corporation) applied to the inner side surface at a constant pressure of 1 mm was read, and the difference between the maximum value and the minimum value was defined as "surface blur".

Test sample (2)-Molded product shown in Fig. 3-1 and Fig. 3-2 [Test sample,
Disk part outer diameter 90mm, thickness 1.5mm, cylindrical part outer diameter 25mm, depth 1
3 mm] was molded and produced under the following two conditions.

Molding conditions Molding machine; Toshiba IS-90B Cylinder temperature; about 200 ° C Mold temperature; about 60 ° C Injection pressure; 670 kg / cm ² Boost time; Condition 5 seconds Condition 11 seconds Cooling time; 10 seconds Measurement method Obtained The surface shake of the test sample (2) 4 was measured as shown in FIG. That is, the test sample is fixed on the fixing table 8 with the weight 5 and a low-pressure probe of a three-dimensional dimension measuring instrument (AE-112 manufactured by Mitutoyo Seisakusho) along the circumference 1.5 mm inside from the outer circumference of the test sample (2) 4. 6 [load 0.30] was applied at 12 points [360 °] every 30 °, and the difference in the vertical direction from a reference point 7 provided at a position 32.5 mm from the outer periphery of the test sample (2) 4 was read. The difference between the maximum value and the minimum value was determined as the surface runout of the test sample (2) 4.

[Thermal stability] Equipment used; DT-30 test manufactured by Shimadzu Corporation; Thermal decomposition rate at 222 ° C (in air atmosphere) [Tensile strength] Measured according to the method of ASTM-D638.

Comparative Examples 1 to 9 Terminally-etherified polyalkylene glycol represented by the general formula R ₁ —O — (— R ₂ —O—) _m —R ₃ , a polyhydric alcohol having 2 to 10 carbon atoms, and a C 22 to 32 carbon atom Of polyhydric alcohol fatty acid esters derived from higher fatty acids of Comparative Example 1 or only one of them was added [Comparative Examples 2, 3, Table 2]. Example 1
And the results shown in Table 4 were obtained. Also,
The same treatment as in Example 1 (Comparative Examples 4 to 9, Table 2) was carried out using compounds other than the above, and the results shown in Table 4 were obtained.

Examples 13 and 14 and Comparative Example 10 A test was performed in the same manner as in Example 1 except that the acetal resin was an oxymethylene homopolymer in which the terminal hydroxyl group was acetylated with acetic anhydride of [η] = 1.3 dl / g. The results are shown in Examples 13 and 14, and the compositions used are shown in Table 1 and the test results are shown in Table 3.

Table 4 shows the results of a test performed in the same manner as in Example 1 using the same oxymethylene homopolymer as in Examples 13 and 14 and without adding any compound other than the thermal oxidation stabilizer.

[Brief description of the drawings]

FIG. 1-1 is a conceptual diagram showing a cross section of a molded article test sample (1). FIG. 1-2 is a plan view of a molded article test sample (1). The crosses in the figure indicate the positions of the pin gates having a diameter of 0.6 mm. FIG. 2 is a schematic view of an apparatus [method] for measuring surface runout of a molded article test sample (1). FIG. 3-1 is a conceptual diagram showing a cross section of a molded article test sample (2). FIG. 3-2 is a plan view of a molded article test sample (2). The crosses in the figure indicate the positions of the pin gates having a diameter of 0.5 mm. FIG. 4 is a schematic view of an apparatus [method] for measuring the surface shake of a molded article test sample (2). DESCRIPTION OF SYMBOLS 1 ... Molded product test sample (1) 2 ... Cylindrical jig 3 ... Measurement terminal of digital micrometer 4 ... Molded product test sample (2) 5 ... Weight 6 ... Low pressure probe of three-dimensional dimension measuring device 7 …… Reference point of 3D dimension measuring device 8 …… Fixing table for test sample

Continuation of the front page (56) References JP-A-63-218756 (JP, A) JP-A-2-263856 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08L 59 / 00-59/04 C08K 5/10-5/103 C08J 5/00

Claims (1)

(57) [Claims] (1) R ₁ -O-(-R ₂ -O-) _m -R ₃ [R ₁ is hydrogen or an aliphatic hydrocarbon having 1 to 7 carbon atoms, based on 100 parts by weight of an acetal resin. R ₂ is an ethylene group or a propylene group, and R ₃ is a group having 1 carbon atom.
And m represents an integer of 20 or more.] 0.01 to 5 parts by weight of at least one kind of terminally etherified polyalkylene glycol represented by the following formula: An acetal resin composition comprising 0.01 to 2.0 parts by weight of at least one polyhydric alcohol fatty acid ester derived from a polyhydric alcohol and a higher fatty acid having 22 to 32 carbon atoms.